This section provides background information related to the present disclosure which is not necessarily prior art.
Medical imaging is broadly used for evaluating the condition of a lesion within a patient. For example, MRI brain images of a patient suffering from an acute stroke such as cerebral infarct or cerebral hemorrhage are taken to evaluate a lesion that is created.
Cho A H, Sohn S I, Han M K, et al. (Safety and Efficacy of MRI-based Thrombolysis in Unclear-Onset Stroke. A preliminary report. Cerebrovasc Dis 2008; 25: 572-579) described a method for estimating an onset time of an infarct region based on MRI FLAIR (fluid-attenuated inversion recovery) images of a patient whose onset time of cerebral infarct is not clear or specified. According to this article, PWI-DWI mismatch (positive perfusion-diffusion mismatch) conditions and FLAIR CHANGE (absence of well-developed fluid-attenuated inversion recovery changes of acute diffusion lesions) conditions are included in MRI-based conditions used as the grounds for estimating an onset time of a cerebral infarct.
However, such conditions including the PWI-DWI mismatch and the FLAIR CHANGE mentioned in the article are empirical indices of physicians that are heavily dependent on visual inspection such that they are less likely to provide quantitative and objective criteria for an accurate decision.
Shlee S. Song, Lawrence L. Latour, Carsten H. Ritter, et al. (A Pragmatic Approach Using Magnetic Resonance Imaging to Treat Ischemic Strokes of Unknown Onset Time in a Thrombolytic Trial. The American Heart Association online Jun. 12, 2012) described a method for estimating an onset time of a cerebral infarct by analyzing brightness (e.g., intensity) in a FLAIR image corresponding to diffusion-positive regions (SIR; Reader-measured signal intensity ratio).
This SIR method still shows limitations to present objective indices because it is rated or graded by a number of image readers to determine an SIR value. Moreover, the SIR method has a limited reliability as it uses one single parameter, i.e., the intensity of a FLAIR image, to determine an onset time of cerebral infarct. Considering that an infarct region has different levels of intensity in the FLAIR image at different times, depending on certain factors, such as, an infarct location, an infarct volume, the age and gender of a patient and so on, subjects show greatly varying levels of intensity. In addition, designating an onset time from a specific SIR value, irrespective of the fact that those time-dependent intensities in the FLAIR image show a spectrum distribution, makes the SIR method less objective as well as less reliable.